El refresco de la masa madre ayuda a la levadura salvaje.

Because this is baking vocabulary.

In everyday Spanish, un refresco often means a soft drink / soda. But in sourdough and bread-making, el refresco de la masa madre means the refreshing / feeding of the starter.

So here refresco is a technical baking term, not a drink.

Because refresco is a masculine noun in Spanish, so it takes el.

• el refresco
• los refrescos

This has nothing to do with masa madre being feminine. The article agrees with refresco, not with the words that come after it.

It is a de phrase attached to refresco.

So:

• el refresco = the refreshment / feeding
• de la masa madre = of the sourdough starter

Together, el refresco de la masa madre means the feeding of the sourdough starter or refreshing the starter.

Here de works a lot like of in English.

Masa madre is the standard Spanish term for sourdough starter.

Literally, it looks like mother dough, but you should learn it as a fixed expression meaning starter. Spanish often uses established compound expressions like this, and they do not always translate word-for-word in a natural way.

The main noun is masa, so the whole expression is feminine:

• la masa madre

Because Spanish uses definite articles more often than English does.

In English, you might say something like Feeding sourdough helps wild yeast, with fewer articles. In Spanish, it is very natural to say:

• El refresco de la masa madre ayuda a la levadura salvaje

Spanish often keeps the article with:

• a specific process: el refresco
• a known noun: la masa madre
• a general category or substance: la levadura salvaje

So the articles sound normal here.

Because ayudar is commonly used with a before the person or thing receiving the help.

So:

• ayudar a alguien
• ayudar a algo

In this sentence:

• ayuda a la levadura salvaje = helps the wild yeast

That a is part of the normal pattern with ayudar.

Because the subject is el refresco, which is singular.

Breakdown:

• El refresco de la masa madre = subject
• ayuda = verb
• a la levadura salvaje = object/complement

Since refresco is singular, the verb must also be singular:

• El refresco ... ayuda

If the subject were plural, then the verb would be plural too:

• Los refrescos de la masa madre ayudan ...

Because in Spanish, descriptive adjectives usually come after the noun.

So:

• la levadura salvaje = the wild yeast

That is the normal order. Putting the adjective after the noun is much more common than in English.

Also, salvaje has the same form for masculine and feminine singular:

• el animal salvaje
• la levadura salvaje

Only the plural changes:

• los animales salvajes
• las levaduras salvajes

Here levadura is being used as a mass/collective idea, similar to yeast in English.

So la levadura salvaje means wild yeast in a general sense, not necessarily one single yeast cell. Spanish often uses the singular for substances or general categories.

You could also find plural forms in more technical contexts, such as las levaduras salvajes, but the singular is perfectly natural here.

It is in the present indicative, and here it most naturally expresses a general truth or general process.

• ayuda = helps

So the idea is:

• Feeding the sourdough starter helps wild yeast

This is not necessarily about one single moment. It sounds like a general statement about how sourdough works.

Yes. The original sentence is understandable and natural in a baking context, but Spanish offers other ways to express the same idea, for example:

• Refrescar la masa madre ayuda a la levadura salvaje.
• El refresco de la masa madre favorece la levadura salvaje.
• Al refrescar la masa madre, se favorece la levadura salvaje.

These are just variations in style. The original sentence is built correctly and clearly.